The present invention concerns the field of the making up of bags of synthetic material or other similar articles into rolls, and has more particularly for its object the provision of a process for winding a predetermined number of bags of synthetic material, previously cut to length and welded, into rolls.
The invention likewise has for its object the provision of a device for carrying out this process.
The currently known processes and apparatuses are based either upon the principle of bags of synthetic material welded and wound into a continuous string from a sheath of synthetic material, or upon the principle of bags made up individually, then folded and stored in cardboard boxes. In the case of bags which are welded and then wound in a string, the separation of one bag from the other on utilisation is effected by unwinding from the roll and by tearing off in the region of a perforation formed in the welding operations. These processes for making up bags in a continuous string possess drawbacks inherent in the actual principle, namely the quality of the weld and the difficulties of tearing away. In fact the preparation of welded and perforated bags in the form of a continuous strip which is then rolled necessitates a certain strip tension, in the course of the manufacturing operations, which is necessary for the conveying of the strip and the actual winding. This strip tension exerts a harmful action upon the regions where the tube is welded transversely to form the bag bottoms. However slight this strip tension may be, it exerts an elongation stress in the region of the weld where the material is softened for purposes of thermo-sealing. The welds thus obtained are weakened and it is practically impossible to obtain welds known as "retracted" which guarantee very good strength behaviour.
Another disadvantage of this process consists in that the tearing off in line with the perforation is not very convenient in fact, especially for certain types of bags either of large format or of great material thickness.
In the case of individually made up bags, the quality of the welds is good and of the "retracted" type, but the folding and storage in cardboard boxes constitutes an irksome operation from the point of view of machinery investment, especially as the operations of folding generally limit the production rates and, for large formats, the folding operations are irksome.
The present invention has the purpose of diminishing the drawbacks of the known processes and apparatuses, while retaining the practicality of bags wound into rolls, starting from individually made up bags, by virtue of a process permitting of obtaining wound rolls comprising a predetermined number of bags previously cut to length and welded by known manufacturing processes.